Satellite technology is being used to assess the prevalence of a parasitic worm which could prove a threat to life.

A research team, based at the Liverpool School of Tropical Medicine, used images taken from space to work out exactly which parts of a large tract of Africa were most likely to be harbouring the worm, called Loa Loa.

Although human infestation by Loa Loa, or eyeworm, can cause health problems, the satellite mapping was needed because the creature is impeding efforts to eradicate a separate illness, called river blindness.

In recent years, a treatment campaign in affected countries has been spectacularly effective in controlling the cause, another parasitic worm called Onchocerca volvulus.

Part of the success was due to the fact that the drug involved, ivermectin, was thought to be so safe that it could be distributed to be used without full medical supervision.

However, when the drug was used in some communities in Cameroon, some of those treated were struck down with a dangerous brain swelling which in some cases proved fatal.

The adverse reaction seemed most likely to occur in communities hardest hit by eyeworm infestation, it was noticed.

Carried by flies

Scientists know that Loa Loa is mainly transmitted by a particular type of fly.

By pinpointing communities lying close to habitats preferred by that fly, those with the highest chance of infestation could be identified.

Then the population could be screened for Loa Loa, and kept under close watch while the river blindness drug was administered.

The satellite images picked out the right type of afforested land, and topography, which, when combined with other data on soil types, rainfall, and temperature, produced a clear "Loa Loa map" of several African countries, including Burkina Faso, Mali and Niger.

Dr Madeleine Thomson, a consultant and lecturer in tropical medicine, was part of the team which analysed the satellite data.

She told BBC News Online: "This is a method which has been used before to predict areas which may have high levels of malaria.

"It's all easy-to-obtain information, much of it on the internet."

She added: "Although the distribution of Loa Loa doesn't necessarily mean that villagers in those areas will have a severe reaction, it allows us to spot which areas need further investigation."

River blindness is caused when the worm involved burrows up under the skin and reaches the eyes.

It is still one of the world's leading causes of blindness.

The worm can also cause severe itching under the skin, and it is hoped that cases can be reduced to only a fraction of previous levels.